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Fixing Appliance Thermostats

If an appliance doesn't heat or cool as it should, check the thermostat.
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Thermostat inside an electric heater.
Thermostats are components in many home appliances. A thermostat is a switch that controls temperature in a heating element or a cooling device. It opens and closes a circuit to supply electric current based on temperature. Thermostats used in appliances may use a bimetal strip, bimetal thermodiscs, or a gas-filled bellows chamber to control the electrical contact. If faulty, they should be replaced rather than repaired.

Many of these mechanical controls have been replaced, or at least assisted, by digital controls. The good news is that digital controls are relatively trouble-free, going many years without service. The bad news is that when they do go out, there's no repair to do; you simply buy another unit and plug it in exactly as the old one. Of course, make sure you've solved any other electrical problems first so the digital controller won't be damaged on installation.

To test and service a large-appliance thermostat:
  1. Unplug and disassemble the appliance enough to access the thermostat.
  2. Hook the clip of the multimeter (see Testing With a Multimeter) to one lead of the thermostat and touch the probe to the other. Or you can touch one probe of the multimeter to each terminal. The reading should be zero.
  3. Turn down the temperature control dial; you'll see the contact points open at the thermostat. The meter should stop buzzing when the contacts open.
  4. If the thermostat is faulty, replace it with a new one, following the manufacturer's instructions.
To test and service a small-appliance thermostat:
  1. Unplug and disassemble the appliance enough to access the thermostat.
  2. Set the multimeter on RX1 scale. Place one probe of the multimeter on the output side and one probe on the input side. The reading should be zero.
  3. Replace the thermostat if faulty.

Text by Dan & Judy Ramsey - from "If It's Broke, Fix It!"
Artwork by Dan & Judy Ramsey
Copyright Fix-It Club® © 2003

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